“We know there were periods when the surface of Mars was frozen; we know there were periods when water flowed freely,” said Briony Horgan with Purdue University at the at the Goldschmidt Geochemistry Conference in Barcelona. “But we don’t know exactly when these periods were, and how long they lasted. We have never sent unmanned missions to areas of Mars which can show us these earliest rocks, so we need to use Earth-bound science to understand the geochemistry of what may have happened there.

“If this is so, it is important in the search for possible life on Mars. We know that the building blocks of life on Earth developed very soon after the Earth’s formation, and that flowing water is essential for life’s development. So evidence that we had early, flowing water on Mars, will increase the chances that simple life may have developed at around the same time as it did on Earth. We hope that the Mars 2020 mission will be able to look more closely at these minerals, and begin to answer exactly what conditions existed when Mars was still young.”

Scientists have long known that water was abundant on ancient Mars, but there has been no consensus on whether liquid water was common, or whether it was largely frozen in ice.

The enduring questions are: Was the temperature high enough to allow the water to flow? Did this happen over an extended period, or just occasionally? Was the surface a desert or frozen? Warm conditions make it much more likely that life would have developed independently on the surface of ancient Mars.

In 2013, Planetary scientists at the European Space Agency released 3D images of the “striking upper part of the Reull Vallis region of Mars”, which reveal a 1500 kilometer long river running from the Promethei Terra Highlands to the vast Hellas basin.

The image data from ESA’s Mars Express spacecraft shows that, at some points, the river bed is 7 kilometers wide and 300 meters deep. The stereo cameras on board the satellite have also revealed “numerous tributaries” that fed the gigantic river.

On the right of the images you can see the Promethei Terra Highlands’s mountains, “rising around 2500m above the surrounding flat plains”. A spectacular landscape not very different from many on Earth.

The ESA Mars Express team said that the river was flowing with abundant water about 3.5 to 1.8 billion years ago, during the Hesperian period. After that, the Amazonian era started, causing the Reull Vallis to be invaded by a glacier.

Early Earth as a Model

Now a new comparison of patterns of mineral deposition on the red planet with similar depositions on Earth lends weight to the idea that early Mars had one or more long periods dominated by rainstorms and flowing water, with the water later freezing.

Our study of weathering in radically different climate conditions such as the Oregon Cascades, Hawaii, Iceland, and other places on Earth, can show us how climate affects pattern of mineral deposition, like we see on Mars. Here on Earth, we find silica deposition in glaciers which are characteristic of melting water. On Mars, we can identify similar silica deposits in younger areas, but we can also see older areas which are similar to deep soils from warm climates on Earth. This leads us to believe that on Mars 3 to 4 billion years ago, we had a general slow trend from warm to cold, with periods of thawing and freezing.

Analysis of the surface geology of Mars supports a trend from a warm to a cold climate, but the climate models themselves don’t support this, due to the limited heat arriving from the young Sun. “If our findings are correct, then we need to keep working on the Mars climate models, possibly to include some chemical or geological, or other process which might have warmed the young planet,” said Horgan.

The research team compared Earth data to Martian minerals detected using the NASA CRISM spectrometer, currently orbiting Mars, which can remotely identify surface chemicals where water once existed. They also took data from the Mars Curiosity Rover. Professor Horgan is a co-investigator on the Mars 2020 mission, due to be launched in July 2020 and to begin to explore the Jezero Crater in February 2021.

The image at the top of the page show the grooved channels of an ancient river delta thread through Jezero crater on Mars. The paleochannel system is one of the hundred analyzed. Credit: NASA/JPL-Caltech/MSSS/JHUAPL